Basic oxygen furnaces are typically used in an integrated steel mill to turn carbon-rich molten pig iron into steel. Raw materials including iron ore, limestone, and coal, coke, and fluxing agents are charged in batches in a blast furnace, which produces molten iron. Generally, molten iron from a blast furnace is poured into a ladle. A basic oxygen furnace is then used to convert the molten iron, along with steel scrap and alloys into refined steel. Substantially pure oxygen is blown onto the steel and iron, igniting the carbon dissolved in the steel and burning it to form carbon monoxide and carbon dioxide. The ore gives up excess oxygen and becomes liquid iron. The burning brings the temperature up to approximately 1700 degrees C. and melts the scrap. Other processes may be included, such as adding flux, to remove impurities. The resulting steel is then poured from these ladles. The process is known as basic due to the pH of the refractories—calcium oxide and magnesium oxide—that line the vessel to withstand the high temperature of molten metal. Electric arc furnaces may also be used.
The basic oxygen furnace, and the electric arc furnace both produce significant waste heat and fuel, in the form of carbon monoxide through the exhaust gas. The reaction that allows the steel to liquefy uses direct injection of oxygen and results in extremely hot, dirty gas released into the atmosphere. Difficulties arise in recovering this energy because of the cyclical nature of the system causing rapid changes in temperature that create thermal shock to equipment. A large volume of particulate is also entrained in the hot exhaust gas that can coat heat transfer surfaces, causing reductions in energy capture and mechanical failures. It has generally been concluded that the severity of the environment precludes the use of heat recovery. The US EPA, in the US EPA Energy Trends in Selected Manufacturing Sectors: Opportunities and Challenges for Environmentally Preferable Energy Outcomes, dated March 2007, indicates a low potential for heat recovery in electric arc furnace heat recovery due to the low demand for steam and waste heat is difficult to recover. With the greater temperature fluctuation and higher particulate loading in the blast furnace, it is likely that the conclusion would be the same.
Therefore, the focus presently is on recovering carbon monoxide gas and pre-heating scrap. However, both of these areas represent lower energy recovery and benefits that preclude the burning of blast furnace waste gas. There are many other disadvantages, including high energy consumption at the induced draft (ID) fan, natural gas consumption at the bypass flare, poor particulate removal, and high greenhouse gas emissions.
Currently, there are approximately 25 basic oxygen steelmaking facilities in North America that utilize about 56 furnaces. These facilities have an approximate capacity of 69.8 million tons/year with an estimated 0.7 mmBtu's wasted per ton of steel produced. There are approximately 72 facilities using electric arc furnaces, with an approximate total capacity of 69.5 million tons/year with an estimated 0.341 mmBtu wasted per ton of steel produced. Therefore, a total of approximately 72.5 million mmBtu of energy is lost per year. Developing this potential energy reserve could produce an average of 15 MW at 97 facilities, offsetting over $500 million/year of electrical generation costs, and over 4 million tons of carbon dioxide production per year. However, modifying the standard exhaust gas treatment from steel production present challenges, including the extreme variability of temperature in the gas stream (potentially over 800° C.), and the very high particulate loading entrained in the gas. Specifically, thermal stress causes refractory to crack, and metallurgy to grow rapidly, resulting ultimately in mechanical failure. Heavy particulate loading coats heat transfer surfaces and erodes insulation and piping in high velocity areas.
Examples of steel furnaces, steel making processes, and pollution control in steel processes may be found in, for example, U.S. Pat. No. 4,072,299 to Calderon, entitled “Method and Apparatus for Basic Oxygen Steel Making Employing the Off-Gas Principle of Pre-Heating Purposes,” issued Feb. 7, 1978; U.S. Pat. No. 5,407,179 to Whipp, entitled “Fluidized Bed Direct Steelmaking Plant,” issued Apr. 18, 1995; U.S. Pat. No. 3,887,340 to Hsu et al., entitled “Method for Scrubbing Gases Derived from Basic Oxygen Furnaces,” issued Jun. 3, 1975; U.S. Pat. No. 4,840,355 to LaBate, entitled “Slag Controlling Device for Basic Oxygen Furnaces,” issued Jun. 20, 1989; U.S. Pat. No. 4,653,064 to Hixenbaugh, entitled “Gas Collector for Metallurgical Vessels,” issued Mar. 24, 1987; U.S. Pat. No. 4,035,179 to Calderon, entitled “Method and Apparatus for Controlling Pollution in Steel Furnaces,” issued Jul. 12, 1977; U.S. Pat. No. 6,241,805 to Lynn et al., entitled “Method and System for Improving the Efficiency of a Basic Oxygen Furnace,” issued Jun. 5, 2001; U.S. Pat. No. 4,373,949 to Spruell et al., entitled “Method for Increasing Vessel Lining Life for Basic Oxygen Furnaces,” issued Feb. 15, 1983; U.S. Pat. No. 6,562,101 to Price et al., entitled “Processing Electric Arc Furnace Dust Through a Basic Oxygen Furnace,” issued May 13, 2003; U.S. Pat. No. 3,741,557 to Harbaugh et al., entitled “Apparatus for Control of Carbon Content in Steel Produced in Basic Oxygen Furnace Process,” issued Jun. 26, 1973; U.S. Pat. No. 5,560,762 to Bresser et al., entitled “Process for the Heat Treatment of Fine-Grained Iron Ore and for the Conversion of the Heat Treated Iron Ore to Metallic Iron,” issued Oct. 1, 1996; U.S. Pat. No. 5,785,733 to Lee et al., entitled “Fluidized Bed Type Reduction Apparatus for Iron Ore Particles and Method for Reducing Iron Ore Particles Using the Apparatus,” issued Jul. 28, 1998; U.S. Pat. No. 5,833,734 to Cip et al., entitled “Process for the Direct Reduction of Particulate Iron-Containing Material and a Plant for Carrying Out the Process,” issued Nov. 10, 1998; U.S. Pat. No. 6,129,888 to Goldstein et al., entitled “System and Method for Minimizing Slag Carryover During the Taping of a BOF Converter in the Production of Steel,” issued Oct. 10, 2000; U.S. Pat. No. 5,968,227 to Goldstein et al., entitled “System and Method for Minimizing Slag Carryover During the Tapping of a BOF Converter in the Production of Steel,” issued Oct. 19, 1999; U.S. Pat. No. 4,679,774 to Lawrence et al., entitled “Fluid Conduit Coupling for a Metallurgical Converter Trunnion,” issued Jul. 14, 1987; U.S. Pat. No. 3,870,507 to Allen, entitled “Control of Pollution by Recycling Solid Particulate Steel Mill Wastes,” issued Mar. 11, 1975; U.S. Pat. No. 3,955,964 to MacDonald et al., entitled “Process for Making Steel,” issued May 11, 1976; and U.S. Pat. No. 6,521,170 to Stercho, entitled “Revamping of a Basic Oxygen Furnace Installation to Provide an Electric Furnace Facility,” issued Feb. 18, 2003. Each of the foregoing references are incorporated by reference in its entirety into this application.